In our U.S. Pat. No. 8,072,684, “Optical Device Using Diffraction Gratings”, issued Dec. 6, 2011, we show how a single-groove diffraction grating with periodic elements of uniform width can be used to couple first order diffraction components of normal s-polarized incident light into a substrate at angles greater than the critical angle of the substrate boundary thereby to cause the diffracted light to propagate through the substrate.